This project involves basis studies of Trypanosoma cruzi, the obligate intracellular protozoan parasite that causes Chagas' disease. A major goal in an elucidation of the genetic diversity of the species and the resultant biological expression and implications of this diversity. Consequently, major emphasis has been placed on studies of single-cell-isolate clones of the parasite. It has been extablished that single "strains" of T. cruzi isolated directly from patients are composed of a diverse population of organisms with significant differences in their extra- and intracellular growth rates, transformation potential, total DNA/organism, Gl, S and G2-M phases during growth, antigenic composition, course of infection in inbred mice and ability to infect cells in vitro. This is the first multiparametic demonstration of the innate pluripotentiality of natural T. cruzi populations. N-acetyl-glucosamine has been shown to be the major cell surface monosaccharide in the vertebrate cell receptor complex which influences infection by T. cruzi. None of the monosaccharides which are common constitutents of vertebrate cells glycoproteins influence infection by Toxoplasma gondii.